Bill Flash Card

A spectator takes a card from a deck. Quickly looks at it and returns it to the deck. The performer takes out a bill from their pocket ($20 for example) and tells the participant that if their card isn't in the deck anymore, they get to keep the $20. The performer continues by saying "You can see for yourself, your card is there. It's right there!" And just as the performer says "there", the spectator looks up to see that the $20 bill has just turned into a card...their card that they had selected from the deck just moments ago. And the transformation took place right before their eyes!